Treating liquid for electrophotographic offset master

ABSTRACT

A TREATING LIQUID TO BE EMPLOYED FOR AN ELECTROPHOTOGRAPHIC OFFSET MASTER, WHICH COMPRISES FERROCYANIDE OR FERRICYANIDE, INORGANIC PHOSPHATE, ORGANIC ACID OR INORGANIC ACID, POLYVALENT METALLIC SALT AND CHELATING AGENT.

United States Patent US. Cl. 106-2 8 Claims ABSTRACT OF THE DISCLOSURE A treating liquid to be employed for an electrophotographic offset master, which comprises ferrocyanide or ferricyanide, inorganic phosphate, organic acid or inorganic acid, polyvalent metallic salt and chelating agent.

BACKGROUND OF INVENTION This invention relates to novel desensitization liquids useful for treating electrophotographic paper when it is to be used as a master copy sheet for offset printing.

Electrophotographic copy paper generally comprises a paper substrate coated with a photoconductive layer comprising a photoconductive material such as zinc oxide, or a sulfide, selenide, sulfate, or the like, dispersed in an insulating resinous binder. When such copy paper is to be used as a copy master for offset printing the desired image is formed on the paper in the usual way, but before use the paper or other material having the image impressed thereon is treated with a desensitizing liquid. The purpose of the desensitizing liquid is to treat the photoconductive layer which is hydrophobic or oleophilic so that the printing ink does not stick to the non-image areas.

A variety of treating liquids are available, but none are completely satisfactory. For example, some of them are very good in desensitizing ability, but are unsatisfactory in that the image area on the treated copy master does not have satisfactory ink holding properties. Other liquids produce papers having good ink holding properties in the image area, but they do not completely desensitize the non-image area.

There are so many variable factors in the process of offset printing, for example, the type of press, the speed of operation, the paper being printed, the ink employed, etc., that desensitizing liquids to be satisfactory should have the following properties in the highest possible degree:

(1) Capable of desensitizing the photoconductive layer so that the ink sticks only to the image area;

(2) Does not impede the ink holding capacity of the image area;

(3) Does not enhance emulsification of the ink;

(4) Does not corrode metal parts of the printing press;

(5) Stable to heat and light over a long period of time;

(6) It retains its purity;

(7) Does not deteriorate the printability of the master copy sheet;

(8) Can be used by dipping the master copy sheet in it;

(9) Works efficiently irrespective of the press employed, the kind of ink and the kind of printing paper.

Japanese patent publication No. 44-9045 describes an aqueous desensitizing liquid containing a ferroor ferricyanide, an inorganic phosphate and a polybasic organic acid. This composition is useful as a desensitizing liquid. Its utility is improved by the addition of water soluble salts such as magnesium salts. Such salts remarkably im- 3,764,353 Patented Oct. 9, 1973 prove the ink holding capacity of the image area. It has been found, however, that the use of such salts leads to the gradual formation and precipitation of a water insoluble phosphate and also adversely affects the stability of the ferroand ferricyanide ion to heat and light.

Desensitizing liquids have now been discovered which do not suffer from these defects.

THE INVENTION This invention provides novel desensitizing liquids having improved properties for treating offset masters prepared from electrophotographic papers. Broadly speaking the compositions are aqueous compositions containing a ferrocyanide or ferricyanide salt, a polybasic organic or inorganic acid, a polyvalent metallic salt and a chelating agent. For convenience the ferrocyanide and ferricyanide salts will hereinafter be referred to as iron containing cyanides, and the polybasic organic or inorganic acids, simply as acids.

More specifically, the aqueous treating liquid will contain from about 1% to 6% of an iron containing cyanide, from about 5% to 10% of a phosphate, from about 0.1% to 5% of an acid, from about 0.01% to 1% by weight of a polyvalent metallic salt and from about 0.05% to 2% by weight of a chelating agent, all based on the total weight of the composition.

Suitable inorganic phosphates include ammonium and alkali metal phosphates including mono and dihydrogen phosphates and mixtures thereof. Typically useful compounds include, for example, Na HPO NaH PO (NI-I HPO- and NI-I H PO Typically useful acids include polybasic organic carboxylic acids including alkanoic acids such as malonic, succinic, fumaric and the like, as well as substituted alkanoic acids such as citric. Inorganic acids which may be employed include, especially, mineral acids such as nitric, sulfuric, hydrochloric, and the like.

Any of a wide variety of chelating agents suitable for retaining metallic ions in aqueous solution may be employed. Ethylene diamine tetra-acetic acid (EDTA) and its various derivatives and analogs are useful as are any of the known organic derivatives of phosphonic acid such as aminotrimethylene phosphonic acid. The function of the chelating agent is to chelate the metallic ion so as to prevent the precipitation of an inorganic phosphate salt and to stabilize the iron containing cyanide.

Metallic salts of polyvalent metals which are useful in this invention are preferably water soluble salts of metallic ions having a valence of at least two. Many of them may be further characterized as containing metals which as the free metals have a specific gravity of 5 or more. The salts include, for example, salts of magnesium, calcium, strontinum, barium, aluminum, chromium, cobalt, nickel, zinc, cadmium, and tin. Soluble salts are preferred, water insoluble salts such as phosphates, arsenates, arsenites, carbonates, silicates, and the like, may also be utilized.

The following non-limiting example further illustrates this invention.

EXAMPLE An electrophotographic copying paper was prepared by coating the surface of a paper support previously subjected to waterproof processing with a dispersion obtained by mixing photoconductive zinc oxide with a resinous binder comprising an acrylic resin or silicone resin, siliconemodified acrylic resin, acrylized alkyd resin and styrenebutadiene resin and drying thereafter to form a photoconductive layer. After charging said layer by corona discharge, the photo-image of an original Was exposed thereon, developed with a dry-process developer and fixed by heating, whereby a copied image was formed. Subsequently, by means of desensitizing the non-image area of the photoconductive layer with the respective treating liquids of the present invention described below, an B. set master was prepared. Said offset master was laid on a 4 An aqueous solution containing the foregoing components was mixed with nitric acid to adjust the pH to 3.5. The solution was next mixed with the following substances.

small-sized offset printing press, and printing was perznswodz f {hereby Whlle t fi dipping hqmd prepared Dequest 2000 (a brand name of an organic phosby diluting the respective treating liquid from three to phonate) 1 5 four times of the amount thereof with water.

Treating liquid 1: Treating liquid 5 G- K4Fe(CN)6 5 0 3 )6 N34F(CN)6 Nail IP04 5.0 Y

NH H PO 4.0 NaH PO 5.0 Water 30 Nail-IP04 4-D Water 87.0 An aqueous solution containing the foregoing components was mixed with citric acid to adjust the pH to 5.0. An aqueous solution containing the foregoing com- The solution was then mixed with the following sub ponents was mixed with phosphoric acid to adjust the pH stances: to 5.2. The solution was next mixed with the following G. substances: Mg(COOH) 0.5 G. Dequest 2006 (the brand name of an organic phos- CoCl 0.5 phonate manufactured by Monsanto Chemical Dequest 2000 0.5 Co.) 1.0 Dequest 2006 0.5 Treating liquid 2: EDTA N32 Na Fe(CN) 2.0 The efiiciency of the above described treating liquids is NaI-I PO 4.0 illustrated in the following table where they are com- (NH4)2HPO 6.0 pared with treating liquids of unknown composition cur- Water 86.0 rently available commercially.

Commercial Treating liquid according treating liquids to the present invention Properties A B C 1 2 3 4 5 Others Desensitization ability S U U S S S S S S Ink-holding property U S S S S S S S U Ink-emulsifying property U U S S S S S S S Corrosive effect on metaL.-. None Pos. None None None None None None None Stability U U s s s s s U Deterioration with lapse of tim U U U S S S S S U Degree of dilution for making dipping-liquid- 0) 0) Toxicity None None None None None None Printability (expressed by number of sheets)-. 3,000 2, 500 2,800 3, 500 3, 500 4,000 5,000 e, 000 3,000 Appearance of image after printing U S U S S U 1 5-10 times.

An aqueous solution containing the foregoing com- Remarks ponents was mixed with succinic acid to adjust the pH (1) Desensifization abilit y. This property is determined to solution Was next mlxed Wlth the following by visual estimation of the wetness of the image area and substances G that of the non-image area after rubbing the surface of an O 0 image-formed offset master with absorbent cotton soaked N1(N with a treating liquid. The image area should be wetted EDTA 2 when thus rubbed, but the non-image area should not be wetted.

Treating liquid 3: (2) Ink-holding property: This property is determined by visual estimation of the degree of ink-adhesion on the K Fe(CN) 2.0 image area and the non-image area after rubbing the sur- NHiHzPO1 3 face of an image-formed offset master with absorbent Na HPO 4 0 cotton soaked with a treating liquid and Wet with a print 2 4 ink. The image area should absorb ink when thus rubbed, NaHZPO! but the non-image area should not absorb ink when thus Water 8 0 treated.

(3) Ink-emulsifying property: This property is deter- An aqueous solution containing the foregoing commined by means of mixing a five-times-diluted solution ponents was mixed with adipic acid to adjust the pH to 4.5. of a treating liquid with a specified amount of a printing The solution was next mixed with the following ubink and measuring the amount of the solution when satustances: rated in the ink. The smaller the amount, the better the G, ink-emulsifying property. c c 05 (4) Stability: This property is determined by visual EDTA Na 15 estimation of the degree of precipitation within a freshly 4 prepared treating liquid. T (5) Deterioration with lapse of time: This is deterrea mg lqm mined by exposing the treating liquid to ultraviolet rays at 70 C. in order to observe changes in appearance, for Na4Fe(cN)6 example, the formation of a precipitate. e z s (6) The compositions of commercially available treat- Wat r V V V ,fla 88.0 ing liquids A, B and C are unknown.

(7) Others means treating liquids containing ferrocyanide or phosphate but containing no polyvalent metallic ron.

(8) Formation of image was performed by employing RICOH Electronic Printer S-1.

(9) Printing was performed by RICOH Offset 1000 or A. B. Dick 320.

(10) The marks S and U denote satisfactory and unsatisfactory," respectively.

The copying paper employed for use with the treating liquid of this invention can be subjected to either of dry or wet development, and the image electrophotographically formed thereon is hydrophobic and oleophilic. The image may be simply desensitized by applying a treating liquid of the invention onto the surface of the photoconductive layer thereof with absorbent cotton soaked with said treating liquid. In case of a treating liquid containing no polyvalent metallic ion as shown in the foregoing table for the purpose of comparison, the ink-holding property within the image area is poor, and it frequently happens that the solid image becomes desensitized and with the result that the ink fails to stick. In contrast, the treating liquid according to this invention as illustrated by the above examples demonstrates an excellent efficiency particularly in terms of ink-holding property, stability and the number of sheets which may be printed.

What is claimed is:

1. An aqueous desensitizing liquid for use in an electrophotographic oifset master sheet comprising:

(a) from about 1% to 6% by weight of a cyanide selected from the group consisting of alkali metal salts of ferricyanides and ferrocyanides,

(b) from about 5% to 10% by weight of at least one phosphate selected from the group consisting of alkali metals and ammonium salts of monoand dihydrogen phosphate,

(c) from about 0.1% to 5% by weight of an acid selected from the group consisting of malonic acid, succinic acid, fumaric acid, citric acid, adipic acid, nitric acid, phosphoric acid, sulfuric acid and hydrochloric acid,

(d) from about 0.01% to 0.1% by weight of a metallic salt selected from the group consisting of Ni(NO )2, CaCl ZI13(PO4)2 and C0Cl and (e) from about 0.05% to 2% by weight of a chelating agent selected from the group consisting of ethylene diamine tetra-acetic acid, disodium ethylene diamine tetra-acetic acid, tetrasodium ethylene diamine tetraacetic acid, aminotrimethylene phosphonic acid and the pentasodium salt of aminotrimethylene phosphonic acid, all by weight based on the total weight of the composition.

2. A treating liquid according to claim 1, wherein the cyanide is K Fe(CN) the phosphate is a mixture of Na HPO and NaH PO the acid is citric acid, the metallic salt is Mg(COOH) and the chelating agent is the pentasodium salt of aminotrimethylene phosphonic acid.

3. A treating liquid according to claim 1, wherein the cyanide is Na Fe(CN) the phosphate is a mixture of NaH PO and (NH HPO the acid is succinic acid, the metallic salt is Ni(NO and the chelating agent is disodium ethylene diamine tetra-acetic acid.

4. A treating liquid according to claim 1, wherein the cyanide is K Fe(CN) the phosphate is a mixture of NH H PO Na HPO and NaH PO the acid is adipic acid, the metallic salt is CaCl and the chelating agent is tetrasodium ethylene diamine tetra-acetic acid.

5. A treating liquid according to claim 1, wherein the cyanide is Na Fe(CN) the phosphate is NH H 'PO the acid is nitric acid, the metallic salt is Zn (PO) and the chelating agent is aminotrimethylene phosphonic acid.

6. A treating liquid according to claim 1, wherein the cyanide is a mixture of Na Fe(CN) and Na Fe(CN) the phosphate is a mixture of NH H PO and Na HPO the metallic salt is CoCl and the chelating agent is a mixture of aminotrimethylene phosphonic acid and the pentasodium salt of aminotrimethylene phosphonic acid.

7. An aqueous desensitizing liquid according to claim 1, wherein the pH of said liquid being in the range from about 3.5 to 5.5.

8. An aqueous desensitizing liquid according to claim 1, wherein the alkali metal salts of ferricyanides and ferrocyanides are sodium or potassium salts.

References Cited UNITED STATES PATENTS 2,988,988 6/1961 Kurz 101-451 3,106,157 10/1963 Reithel 101-451 3,152,969 10/1964 Eastman 101-456 X 3,211,686 12/1965 Uber et al. 101-451 X 3,398,002 8/1968 Bondurant et al. 106-2 3,481,271 12/1969 Shimazu 101-453 3,522,062 7/1970 Shimizu et al. 106-2 JOSEPH L. SCHOFER, Primary Examiner J. B. EVANS, Assistant Examiner US Cl. X.R. 

